Polycyclic aromatic hydrocarbons (PAH) are potent carcinogens in rat mammary and other rodent tissues and epidemiological studies link human exposure to PAH-containing mixtures to an increased risk of breast, lung and skin cancer. The goals of this project are to determine how PAH bind to DNA in mammalian cells and to establish the relationship between specific PAH-DNA adducts and the induction of mutations and cancer. Sensitive analytical techniques permit detection of PAH-DNA adducts in tissues from exposed humans, however, in order to relate human exposure to cancer induction it is essential to know the relationship of the formation and repair of specific PAH-DNA adducts to the induction of biological effects. To determine the role of metabolic activation and DNA adduct formation and repair in the induction of biological effects three PAH {benzo[alpha]pyrene (BaP), 7,12-dimethylbenz[alpha]anthracene (DMBA), and dibenzo[alpha,l]pyrene (DB[alpha,l]P), the most carcinogenic environmental PAH} will be studied in human mammary carcinoma cell lines, secondary mammary epithelial cell cultures from humans and rats, and other cells from humans and rodents selected for inducibility of cytochrome P450 isoforms. The following specific aims will be carried out: 1) To characterize the metabolic activation of DB[alpha,l}P in cell cultures derived from human mammary tissue and compare it to that in cells from other species by the use of 33P and 35S-postlabeling and HPLC. 2) To compare the role of specific P450 isoforms and their induction in the metabolic activation of DB{alpha,l}P and BaP by Western blotting, inhibitory antibodies and antisense oligonucleotides. 3) To measure repair of individual BaP-, DMBA-, and DB[alpha,l]P-DNA addicts in human and rat mammary cell cultures and in other human and rodent cell cultures and to establish the role of p3 induction in the recognition and repair of PAH-induced DNA damage. 4) To examine the binding of diol epoxide isomers of DB[alpha,l]P and BaP to duplexes of self complementary oligonucleotides containing dA or dG to assess the role of base sequence in PAH-DNA binding. 5) To compare athe ability of human and rat mammary epithelial cells to activate DB[alpha,l]P in V79 cell-mutation assays. 6) To compare the relative mutagenic potency of dA adducts formed by diol epoxides of fjord-region containing PAH of differing carcinogenic potency in V79 cells. These studies will allow us to determine which pathways of activation and which PAH-DNA adducts are formed in human mammary cells and to establish their potential to induce biological effects. Understanding the differences in PAH activation and PAH-DNA adduct formation and repair between rodent and human cells i mammary and other tissues will make it possible to relate, on a mechanistic basis, the results obtained in rodent bioassays such as mammary tumor induction to the relative risk these PAH pose to human tissues such as breast and skin.